Chemoattractants, hormones, neurotransmitters, odorants and other sensory stimuli exert their effects upon cells through a vast family of serpentine G-protein couple receptors (GPCRs). The mechanisms of G-protein mediated signal transduction have been studied using isolated membranes and purified proteins. These studies have shown that excited receptors catalyze the exchange of GTP for GDP and the dissociation of the G-protein heterotrimer, allowing both the GTP-bound α-subunit and free βγ-complexes to signal to downstream effectors. The intrinsic GTPase activity of the α-subunit hydrolyzes the bound GTP and the heterotrimer reassociates, completing the cycle (1,2). There is a need in the art for a technique to directly monitor subunit dissociation and reassociation in living cells.